There are known methods for electrochemical working of metals, involving forced oscillation of one of the two electrodes used for the purpose. As the electrodes are brought closer together, synchronized voltage pulses are applied thereto; however, the application of pulses is discontinued when the distance between the electrodes is brought to a minimum. The cutoff of voltage at this point significantly affects the rate and accuracy of copying operations.
There is further known an electrochemical working method involving forced oscillation of one electrode which is synchronized with the application of voltage pulses. The on-off time ratio is varied in the course of the process, being low at the start and increasing towards the end of the working. The pulses are shifted in time so as to reduce instantaneous widths of the interelectrode gap at which the gap conducts current. Voltage pulses can be applied to the electrodes both when they are drawn close to each other and when they are brought apart. However, no voltage pulse is applied with the electrodes being at a minimum distance from one the other. The control of the process conditions by shifting pulses in time and varying the on-off time ratio is disadvatageous in that it reduces the accuracy of the working, especially in cases of broaching vertical walls.
Generally, the conventional electrochemical working methods are disadvantageous in a broad range of variations in the width of the interelectrode gap. The application of voltage pulses under such conditions is tantamount to applying them with a large mean gap width and substantially affects the accuracy of copying the tool electrode on the surface being worked.
There is further known a method for controlling the width of the interelectrode gap in the course of electrochemical working which involves forced oscillation of one of the electrodes, synchronized with the application of voltage pulses to said electrodes (cf. USSR Inventor's Certificate No 187,125, Cl. 2G 05 d 3/00). According to this method, additional low-voltage current is applied to the electrodes, and the interelectrode gap width is controlled with reference to surges of this current, caused by short-circuiting of the electrodes.
The foregoing technique of controlling the width of the interelectrode gap with reference to surges of current supplied from a low-voltage source, which surges are brought about by a direct contact between the tool electrode and article being worked, rules out the application of working voltage pulses to the electrodes found at a minimum distance from one the other. The idea is to prevent damaging the tool electrode and surface being worked by short-circuiting. In fact, voltage pulses are applied as the tool electrode is on its way to or from the surface being worked, i.e. at a variable width of the interelectrode gap. In most cases, the oscillation amplitude is about 0.2 mm, and the working voltage on-off time ratio is 2 to 3. These figures clearly suggest that the electrochemical dissolution occurs at a large mean gap width, which reduces the accuracy of the working of articles and, especially, of their side planes. Attampts to improve the accuracy by increasing the on-off time ratio to a value as high as 5 to 10, i.e. by reducing the duration of working voltage pulses, lead to significant drops in the feedrate. It should also be kept in mind that voltage is continuously fed to the electrodes by the auxiliary power source so that the contact between them inevitably causes erosion of both the tool electrode and the workpiece. The contact of the electrodes may also lead to mechanical deformation of the tool electrode and the workpiece, especially when working small cavities or blanks of relatively soft materials.
Thus the conventional electrochemical working and interelectrode gap control methods, based on oscillation of one of the electrodes, which is synchronized with voltage pulses, are inadequate in what concerns the accuracy, effectiveness and quality of working articles of comple configurations.
There are known means for electrochemical working, based on the principle of analyzing high-frequency current components which are brought about by all kinds of process disturbances and may cause short-circuiting in the interelectrode gap.
None of such means can be used for pulse-current electrochemical working, because the high-frequency spectrum of the pulse train suppresses useful signals as a result of microbreakdowns of the interelectrode gap.
There are further known means for electrochemical working, involving the use of an oscillating electrode and pulse current, which operate as controllers in the sense that the automatic advance of one electrode towards the other is discontinued as soon as the electrodes come into contact. Working pulse voltage can only be applied to the electrodes in the process of bringing them closer together or apart, i.e. under the conditions when the interelectrode width is variable within a broad range. Clearly, this serously affects the rate and accuracy of copying operations.